JP2013243329A - Surface emitting laser element and atomic oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emitting laser element which emits a laser beam having a wide divergence angle.SOLUTION: There is provided the surface emitting laser element including a lower DBR formed on a substrate, an active layer formed on the lower DBR, and an upper DBR formed on the active layer. The upper DBR includes a dielectric multilayer film formed by alternately laminating dielectrics having different refractive indices. A light shielding part is formed on the upper DBR. The light shielding part has an opening for emitting light at a central portion thereof.

Description

  The present invention relates to a surface emitting laser element and an atomic oscillator.

  A VCSEL (Vertical Cavity Surface Emitting LASER) is a semiconductor laser that emits light in a direction perpendicular to the surface of a substrate. Compared with an edge-emitting semiconductor laser, it is low in cost, low power consumption, and compact. Therefore, it has the characteristics of high performance and easy integration in two dimensions.

  The surface emitting laser has a resonator structure including a resonator region including an active layer, and an upper reflecting mirror and a lower reflecting mirror provided above and below the resonator region (Patent Document 1). Therefore, in order to obtain light having the oscillation wavelength λ, the resonator region is formed with a predetermined optical thickness so that the light having the wavelength λ resonates in the resonator region. The upper reflecting mirror and the lower reflecting mirror are formed by alternately laminating materials having different refractive indexes, that is, a low refractive index material and a high refractive index material, so that a high reflectance can be obtained at the wavelength λ. In addition, the optical film thickness of the low refractive index material and the high refractive index material is formed to be λ / 4. It has also been proposed to form elements with different wavelengths in the chip (Patent Documents 2, 3, 4, 7).

  Further, there is an atomic clock (atomic oscillator) as a clock for measuring an extremely accurate time, and a technique for downsizing the atomic clock has been studied. An atomic clock is an oscillator based on the amount of transition energy of electrons constituting atoms such as alkali metals, and in particular, the transition energy of electrons in alkali metal atoms is very precise in the absence of disturbance. Since the value is obtained, frequency stability that is several orders of magnitude higher than that of the crystal oscillator can be obtained.

  There are several types of such atomic clocks. Among them, the CPT (Coherent Population Trapping) type atomic clock has a frequency stability that is about three orders of magnitude higher than that of a conventional crystal oscillator, and is ultra-compact. Therefore, ultra-low power consumption can be desired (Non-patent Documents 1 and 2, Patent Document 5).

  In the CPT type atomic clock, as shown in FIG. 1, a light source 910 such as a laser element, an alkali metal cell 940 encapsulating an alkali metal, and a photodetector 950 that receives laser light transmitted through the alkali metal cell 940; The laser beam is modulated, and two transitions of electrons in the alkali metal atom are simultaneously performed and excited by sideband wavelengths appearing on both sides of the carrier wave having a specific wavelength. The transition energy in this transition is invariant, and when the sideband wavelength of the laser light coincides with the wavelength corresponding to the transition energy, a transparency phenomenon occurs in which the light absorption rate in the alkali metal is lowered. In this manner, the wavelength of the carrier wave is adjusted so that the light absorption rate by the alkali metal is lowered, and the signal detected by the photodetector 950 is fed back to the modulator 960, and the modulator 960 This is an atomic clock characterized by adjusting the modulation frequency of the laser light from the light source 910. The laser light is emitted from the light source 910 and applied to the alkali metal cell 940 via the collimating lens 920 and the λ / 4 plate 930.

  As a light source for such an ultra-small atomic clock, a surface emitting laser with a small size and ultra-low power consumption and high wavelength quality is suitable, and the wavelength accuracy of the carrier wave is required to be ± 1 nm with respect to a specific wavelength. (Non-Patent Document 3).

  Further, the frequency stability of the atomic clock is determined by the shorter distance between the diameter of the laser beam passing through the alkali metal cell 940 and the optical path length, and if it is shorter, the stability becomes worse. Therefore, it is preferable that the diameter of the laser beam is as wide as possible.

  However, the divergence angle of the laser light of the surface emitting laser is narrower than that of the end face type laser, and when the frequency stability is increased, the diameter of the laser light passing through the alkali metal cell 940 is increased. The distance X with the lens 920 needs to be long. Therefore, when a surface emitting laser is used as the light source 910, it has been difficult to achieve both the miniaturization of the atomic clock and high frequency stability.

  In addition, surface emitting lasers are manufactured because it is difficult to produce a large amount of surface emitting lasers that oscillate at the same wavelength due to variations in the growth rate of semiconductor layers during manufacturing and uneven distribution of film thickness. There were problems with the reproducibility and uniformity of surface emitting lasers. Specifically, a film formed by a normal MOCVD (Metal Organic Chemical Vapor Deposition) apparatus or MBE (Molecular Beam Epitaxy) apparatus has a film thickness uniformity of about 1% to 2% and a wavelength of 850 nm. When a film having the same thickness as is formed, an in-plane distribution of 8.5 nm to 17 nm is generated. Therefore, in an application where about ± 1 nm with respect to the wavelength is required, the yield is low and the cost is high.

  The present invention has been made in view of the above, and an object thereof is to provide a surface emitting laser having a wide divergence angle. Another object of the present invention is to provide a surface-emitting laser element having a surface-emitting laser that emits light having a predetermined wavelength and a wide divergence angle at low cost. It is another object of the present invention to provide an atomic oscillator that achieves both downsizing and high frequency stability, and further provides a low-cost and high-accuracy atomic oscillator.

  The present invention includes a lower DBR formed on a substrate, an active layer formed on the lower DBR, and an upper DBR formed on the active layer, the upper DBR having a refractive index. It includes a dielectric multilayer film formed by alternately stacking different dielectrics, and a light shielding part is formed on the upper DBR, and light is applied to the central part of the light shielding part. It has the opening part for radiate | emitting, It is characterized by the above-mentioned.

  The present invention also includes a lower DBR formed on a substrate, an active layer formed on the lower DBR, and an upper DBR formed on the active layer, and the upper DBR is refracted. A dielectric multilayer film formed by alternately laminating dielectrics having different rates, wherein a light-shielding portion is formed on the active layer and below the dielectric multilayer film. The light-shielding portion has an opening for emitting light at a central portion.

Further, the present invention is characterized in that the light emitted from the opening by the light-shielding portion has an intensity (divergence angle) of 20 degrees or more at an intensity 1 / e ² .

Further, the invention is characterized in that the area of the opening is 30 μm ² or less.

In the present invention, the area of the opening is 20 μm ² or less.

  Further, the present invention is characterized in that the light shielding part is formed of a metal material or a material that absorbs the light.

  In the present invention, a contact layer is formed between the active layer and the dielectric portion of the upper DBR, and one electrode is connected to the contact layer.

  The present invention further includes a wavelength adjustment layer between the active layer and the dielectric portion of the upper DBR, and a plurality of different wavelengths are emitted by changing the thickness of the wavelength adjustment layer. It is characterized by having a surface emitting laser.

  According to the present invention, a contact layer is formed between the active layer and the wavelength adjusting layer, and one electrode is connected to the contact layer.

  Further, the present invention is characterized in that the contact layer is formed of a material containing GaAs.

  According to the present invention, the wavelength adjustment layer is formed of a film in which GaInP and GaAsP are alternately stacked, or a film in which GaInP and GaAs are alternately stacked. The thickness of the wavelength adjusting layer is changed by removing the portion for each layer.

  Further, according to the present invention, the stacked film in the wavelength adjustment layer is removed by wet etching, and the first etching solution for removing the GaInP and the GaAsP or the GaAs are used. The second etchant for etching is different from the second etchant.

  According to the present invention, the substrate is a conductive semiconductor crystal substrate, and the lower DBR, the active layer, and the wavelength adjustment layer are formed by epitaxially growing a semiconductor material. Features.

  In the invention, it is preferable that the plurality of surface emitting lasers emit light having different wavelengths.

  The present invention is characterized in that the plurality of surface emitting lasers include a plurality of surface emitting lasers that emit light having the same wavelength.

  In the invention, it is preferable that any one of the plurality of wavelengths is 780.2 nm, 795.0 nm, 852.3 nm, and 894.6 nm.

  In the invention, it is preferable that the dielectric contains an oxide, a nitride, or a fluoride.

  Further, the present invention is characterized in that the active layer contains GaInAs.

  In addition, the present invention is characterized in that the size of the substrate is smaller than 500 μm × 500 μm.

  The present invention also relates to the surface-emitting laser element described above, an alkali metal cell encapsulating an alkali metal, and the alkali metal cell among the light irradiated to the alkali metal cell from the surface-emitting laser in the surface-emitting laser element. A light detector that detects the light transmitted through the surface emitting laser, and two types of light including two sidebands emitted from the surface emitting laser are incident on the alkali metal cell. The modulation frequency is controlled by the light absorption characteristic by the quantum interference effect by the resonant light.

  Further, the present invention is characterized in that the two light beams having different wavelengths are sideband light beams emitted from the surface emitting laser.

  In the present invention, the alkali metal is rubidium or cesium.

  According to the present invention, a surface emitting laser having a wide divergence angle can be provided. In addition, a surface-emitting laser element having a surface-emitting laser that emits light having a predetermined wavelength and a wide divergence angle can be provided at low cost. In addition, it is possible to provide an atomic oscillator in which both miniaturization and high frequency stability are compatible, and further, it is possible to provide a low-cost and high-precision atomic oscillator.

Illustration of atomic oscillator Structure diagram of surface emitting laser element in first embodiment Correlation diagram between area of opening and FFP (1) Correlation diagram between area of opening and FFP (2) Correlation diagram of opening diameter and FFP Top view of surface emitting laser element according to second embodiment Explanatory drawing of the surface emitting laser element in 2nd Embodiment Explanatory drawing (1) of the manufacturing method of the surface emitting laser element in 2nd Embodiment Explanatory drawing (2) of the manufacturing method of the surface emitting laser element in 2nd Embodiment Explanatory drawing (3) of the manufacturing method of the surface emitting laser element in 2nd Embodiment Structure diagram of surface emitting laser element in second embodiment Structural diagram of surface emitting laser element according to third embodiment Correlation diagram between area of upper electrode opening of surface emitting laser element and FFP in third embodiment Top view of surface emitting laser element according to the fourth embodiment Top view of surface emitting laser element in fifth embodiment Explanatory drawing of the atomic oscillator in the sixth embodiment Structural diagram of atomic oscillator in sixth embodiment Explanatory diagram of atomic energy level explaining CPT method Illustration of output wavelength during surface emitting laser modulation Correlation diagram between modulation frequency and amount of transmitted light

  The form for implementing this invention is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
The surface-emitting laser element in the first embodiment will be described with reference to FIG. The surface emitting laser element in the present embodiment is formed by laminating a lower DBR 102, an active layer 103, a contact layer 105, and an upper DBR 106 on a substrate 101 made of a semiconductor or the like. 107 is formed.

  The lower DBR 102 is formed by alternately stacking semiconductor layers having different refractive indexes.

  The active layer 103 is formed with a predetermined thickness on the lower DBR 102, and a current confinement layer is formed therein. The current confinement layer includes a selective oxidation region 123a that is selectively oxidized from the surroundings and a current confinement region 123b that is not selectively oxidized, and current flows in a concentrated manner in the current confinement region 123b.

  The contact layer 105 is formed on the active layer 103 and is made of a semiconductor material. The lower DBR 102, the active layer 103, and the contact layer 105 are formed by epitaxially growing a semiconductor material, and a resonator region is formed by the active layer 103 and the contact layer 105.

  The upper DBR 106 is formed on the contact layer 105. The upper DBR 106 is formed of a dielectric film such as an oxide, nitride, or fluoride, and is formed by alternately stacking a high refractive index material film and a low refractive index material film. In this embodiment, since the lower DBR 102 and the upper DBR 106 have a function as a mirror, the lower DBR may be described as a lower reflecting mirror and the upper DBR may be described as an upper reflecting mirror.

  In the surface emitting laser element according to the present embodiment, the wavelength of the emitted laser light is substantially determined by the thickness of the resonator region between the lower DBR 102 and the upper DBR 106.

  Further, an upper electrode 131 is formed around the upper DBR 106 on the contact layer 105, and the active layer 103 between the lower electrode (not shown) formed on the back surface of the substrate 101 and the upper electrode 131 is formed. In this structure, a current is supplied. In addition to the back surface of the substrate 101, the lower electrode may have a structure provided on the upper surface as long as current can flow through the active layer 103.

  In the surface emitting laser element according to the present embodiment, a light shielding portion 107 is formed on the upper DBR 106. The light shielding part 107 has an opening 108 in the central part of the upper DBR 106. The light shielding portion 107 is formed of a metal material, and is formed of, for example, a laminated film of Cr (lower layer) and Au (upper layer). Therefore, in the surface emitting laser element according to the present embodiment, light having a wavelength λ is emitted from the opening 108. The reason why Cr is used as a lower layer is to improve the adhesion with the dielectric film forming the upper DBR 106, and Ti or the like may be used instead of Cr. Thus, by forming the light shielding part 107 having the opening 108 on the upper DBR 106, the divergence angle of the light emitted from the opening 108 can be widened.

This will be described with reference to FIG. FIG. 3 shows the relationship between the area of the opening 108 and FFP (Far Field Pattern: may be described as a divergence angle in this embodiment), and the area of the current confinement region 123b is changed. Indicates. In FIG. 3, for convenience, the oscillation wavelength of the surface emitting laser is 780 nm (in the atomic oscillator described later, the wavelength corresponding to the Db line of Rb), and the upper DBR is formed of a laminated film of semiconductor materials having different refractive indexes. FFP is a value at 1 / e ² . The current confinement region 123b and the opening 108 are both formed in a rectangular shape, and the output of the laser beam is 0.3 mW, which is the operation in the basic mode.

As shown in FIG. 3, the FFP value is low when the area of the opening 108 is wide, and the FFP value is high when the area of the opening 108 is narrowed. Therefore, by reducing the area of the opening 108, the FFP value can be increased and the divergence angle can be increased. In the case shown in FIG. 3, when the area of the opening 108 is 20 μm ² or less, the FFP value is 20 ° or more, and when it is 10 μm ² or less, the FFP value is 30 ° or more.

  In a normal surface emitting laser element, the opening area is about 100 μm, and according to FIG. 3, the FFP is about 12 °. The distance from the exit where the beam diameter is Φ1 mm is about 4.8 mm. On the other hand, when FFP is 20 °, it can be shortened to about 2.8 mm.

  The FFP value also depends on the area of the current confinement region 123b. By narrowing the area of the current confinement region 123b, the FFP value increases, but the FFP value depends on the area of the opening 108. Sexuality is higher. Note that, when the thickness of the oxide film in the selective oxidation region 123a increases, the light confinement becomes stronger, so the FFP value increases. However, when the thickness of the oxide film is increased, the surface emission occurs due to the distortion caused by the oxide film. The laser element is easily destroyed. 3 and the like show a case where the thickness of AlAs, which is a selective oxidation layer for forming an oxide film in the selective oxidation region 123a, is 32 nm.

  FIG. 4 shows the relationship between the area of the opening 108 and the FFP when the shape of the opening 108 is circular and rectangular. As shown in FIG. 4, the FFP hardly depends on the shape of the opening 108 and depends on the area of the opening 108.

  FIG. 5 shows a case where the opening 108 is circular and shows the relationship between the diameter of the opening 108 and the FFP, and shows a case where the area of the current confinement region 123b is changed. The value of FFP is increased by shortening the diameter of the opening 108, which is the same tendency as when the area of the opening 108 is reduced.

  As described above, by providing the light shielding portion 107 having the opening 108, the divergence angle of the laser light emitted from the surface emitting laser can be widened. In the surface emitting laser according to this embodiment, the center of the current confinement region 123b and the center of the opening 108 are formed so as to overlap in the light emitting direction.

  In the present embodiment, since the light shielding portion 107 is formed to block light, the size of the region where the upper DBR 106 is formed is different from the case where the upper electrode is formed on the upper DBR 106. Even if it is made small, there is no problem in the function as the light shielding portion 107.

  In the present embodiment, the light shielding portion 107 may be formed of a material that absorbs light. By forming the light shielding portion 107 with a material that absorbs light, reflection of light from the light shielding portion 107 can be prevented, and the laser oscillation condition can be prevented from being changed by such reflected light. it can.

  In Patent Document 6 (Japanese Patent Application Laid-Open No. 2002-208755), the lower DBR, the active layer, and the upper DBR are all formed of a semiconductor, and an upper electrode having a narrow opening is formed on the upper DBR, so that the basic transverse mode output of the surface emitting laser is obtained. There is an example of extracting selectively. According to this, as shown in FIG. 22 of Patent Document 6, the divergence angle depends on the upper electrode opening diameter and has a minimum point. The divergence angle is expanded by narrowing the upper electrode opening to the same extent as the current injection region. On the other hand, the divergence angle is also widened when the upper electrode opening is wide, which is due to higher order mode oscillation. In the present invention, the upper DBR is a dielectric, the lower part of the light shielding part is a dielectric, the light shielding part is not in direct contact with the contact layer, and the upper electrode formed on the contact layer is the light shielding part. This is different from Reference 6.

  According to the present invention, even when the upper DBR is formed of a dielectric, the divergence angle can be widened by the light shielding portion.

[Second Embodiment]
(Structure of surface emitting laser element)
Next, a surface emitting laser element according to the second embodiment will be described. As shown in FIGS. 6 and 7, the surface emitting laser element in the present embodiment has a plurality of surface emitting lasers. Specifically, the first surface emitting laser 11 and the second surface emitting laser. A laser 12, a third surface emitting laser 13, and a fourth surface emitting laser 14 are provided. FIG. 7 is simplified for the description of the present embodiment, and the description of the contact layer, the selective oxidation region, and the like is omitted for convenience.

  The 1st surface emitting laser 11, the 2nd surface emitting laser 12, the 3rd surface emitting laser 13, and the 4th surface emitting laser 14 are connected to the electrode pad provided corresponding to each. Specifically, an electrode pad 21 is connected to the first surface emitting laser 11, an electrode pad 22 is connected to the second surface emitting laser 12, and the third surface emitting laser 13 is connected to the third surface emitting laser 13. An electrode pad 23 is connected, and an electrode pad 24 is connected to the fourth surface emitting laser 14. The first surface-emitting laser 11, the second surface-emitting laser 12, the third surface-emitting laser 13, and the fourth surface-emitting laser 14 have different wavelengths of emitted light. . That is, the wavelength λ1 emitted from the first surface emitting laser 11, the wavelength λ2 emitted from the second surface emitting laser 12, the wavelength λ3 emitted from the third surface emitting laser 13, and the fourth surface emitting laser. The wavelength λ4 emitted from 14 is different from each other.

  In order to make the wavelengths λ1 to λ4 different from each other in this way, as shown in FIG. 7, in the first surface emitting laser 11 to the fourth surface emitting laser 14, between the active layer 103 and the upper DBR 106 The wavelength adjustment layers 110 having different film thicknesses are formed. That is, in the case where the lower DBR 102 is formed on the substrate 101 and the active layer 103, the wavelength adjusting layer 110, and the upper DBR 106 are formed on the lower DBR 102, the light having the wavelength emitted from each surface emitting laser is the same as the lower DBR 102. It depends on the thickness of the resonator region between the upper DBR 106 and the upper DBR 106. Therefore, in FIG. 7, since the resonator region is formed by the active layer 103 and the wavelength adjustment layer 110, the thickness of the wavelength adjustment layer 110 is different for each surface emitting laser. The thickness of the resonator region in the light emitting laser can be changed, and the wavelength of light emitted from each surface emitting laser can be set to a different wavelength.

  Specifically, a lower DBR 102 is formed by alternately stacking semiconductor materials having different refractive indexes on a substrate 101 made of a semiconductor or the like, and an active layer 103 having a predetermined thickness is formed on the lower DBR 102. Form. On the active layer 103, a wavelength adjustment layer 110 having a different thickness is formed for each semiconductor laser. The wavelength adjustment layer 110 is formed by laminating a first adjustment layer 111, a second adjustment layer 112, a third adjustment layer 113, and a fourth adjustment layer 114 on the active layer 103. The first adjustment layer 111 and the third adjustment layer 113 are made of the same material, and the second adjustment layer 112 and the fourth adjustment layer 114 are made of the same material. Specifically, one of the two types of materials forming the first adjustment layer 111 to the fourth adjustment layer 114 is made of GaInP, and the other is made of GaAsP or GaAs. The lower DBR 102, the active layer 103, and the wavelength adjustment layer 110, which are semiconductor layers formed on the substrate 101, are formed by epitaxially growing a semiconductor material.

  On the wavelength adjustment layer 110, the upper DBR 106 is formed for each surface emitting laser. The upper DBR 106 is a dielectric film made of oxide, nitride, fluoride, or the like, and is formed by alternately stacking high refractive index material films and low refractive index material films.

  On the upper DBR 106, as in the first embodiment, a light shielding portion 107 having an opening 108 in the center is formed. The light shielding portion 107 is formed of a metal material, and is formed of, for example, a laminated film of Cr (lower layer) and Au (upper layer). In the present embodiment, light from the surface emitting laser element is emitted from the opening 108. The reason why Cr is used as a lower layer is to improve the adhesion with the dielectric film forming the upper DBR 106, and Ti or the like may be used instead of Cr. In the surface emitting laser according to the present embodiment, only the light shielding portion 107 is formed on the upper DBR 106 without forming the upper electrode 131. Thus, by forming the light shielding part 107 having the opening 108 on the upper DBR 106, the divergence angle of the light emitted from the opening 108 can be widened.

  Thus, in the present embodiment, in the first surface emitting laser 11, the first adjustment layer 111, the second adjustment layer 112, the third adjustment layer 113, and the fourth adjustment layer 110 are included in the wavelength adjustment layer 110. The adjustment layer 114 is formed, and the first adjustment layer 111, the second adjustment layer 112, the third adjustment layer 113, the fourth adjustment layer 114, and the active layer 103 form a resonator region. Therefore, the first surface-emitting laser 11 emits light having a wavelength λ1 corresponding to the thickness of the resonator region in the first surface-emitting laser 11.

  In the second surface emitting laser 12, the first adjustment layer 111, the second adjustment layer 112, and the third adjustment layer 113 are formed in the wavelength adjustment layer 110, and the first adjustment layer 111 is formed. The resonator region is formed by the second adjustment layer 112, the third adjustment layer 113, and the active layer 103. Therefore, the second surface emitting laser 12 emits light having a wavelength λ2 corresponding to the thickness of the resonator region in the second surface emitting laser 12.

  In the third surface emitting laser 13, the first adjustment layer 111 and the second adjustment layer 112 are formed in the wavelength adjustment layer 110, and the first adjustment layer 111 and the second adjustment layer 112 are formed. A resonator region is formed by the active layer 103. Therefore, the third surface emitting laser 13 emits light having a wavelength λ3 corresponding to the thickness of the resonator region in the third surface emitting laser 13.

  In the fourth surface emitting laser 14, the first adjustment layer 111 of the wavelength adjustment layer 110 is formed, and the first adjustment layer 111 and the active layer 103 form a resonator region. Therefore, the fourth surface emitting laser 14 emits light having a wavelength λ4 corresponding to the thickness of the resonator region in the fourth surface emitting laser 14.

  As described above, in the surface emitting laser element according to the present embodiment, a plurality of surface emitting lasers that emit light having different wavelengths can be formed on one substrate 101. Therefore, even when a film thickness variation occurs in the semiconductor layer or the like when manufacturing the surface emitting laser element, the first surface emitting laser 11 emits light having a wavelength closest to the desired wavelength. By selecting one of the four surface emitting lasers 14, a semiconductor laser having a desired wavelength can be easily obtained. Thereby, a surface emitting laser element having a surface emitting laser that emits light at a predetermined wavelength can be manufactured at low cost. In the surface emitting laser element according to the present embodiment, each surface emitting laser has a wide divergence angle, and thus has the same effect as that of the first embodiment.

(Method for forming wavelength adjustment layer in surface emitting laser element)
Next, a method for forming a wavelength adjustment layer in the surface emitting laser element according to the present embodiment will be described.

  First, as shown in FIG. 8A, a lower DBR 102 made of a semiconductor material, an active layer 103, and a wavelength adjustment layer 110 are formed on a substrate 101 by epitaxial growth using MOCVD or MBE. The wavelength adjustment layer 110 is formed by laminating a first adjustment layer 111, a second adjustment layer 112, a third adjustment layer 113, and a fourth adjustment layer 114. Here, the first adjustment layer 111 and the third adjustment layer 113 are made of GaInP, and the second adjustment layer 112 and the fourth adjustment layer 114 are made of GaAsP. In this embodiment, the optical thickness of the resonator region is 3λ with respect to the oscillation wavelength λ.

  Next, as shown in FIG. 8B, a resist pattern 151 is formed in a region where the first surface emitting laser 11 is formed. Specifically, a resist pattern 151 is formed by applying a photoresist on the fourth adjustment layer 114 of the wavelength adjustment layer 110 and performing exposure and development with an exposure apparatus.

  Next, as shown in FIG. 8C, the fourth adjustment layer 114 in a region where the resist pattern 151 is not formed is removed by wet etching. Specifically, since the fourth adjustment layer 114 is formed of GaAsP, wet etching is performed using a mixed solution of sulfuric acid, hydrogen peroxide, and water. As a result, only the fourth adjustment layer 114 in a region where the resist pattern 151 is not formed is removed, and the surface of the third adjustment layer 113 is exposed. This mixed solution can etch GaAsP, but GaInP forming the third adjustment layer 113 can hardly be etched. This mixed solution may be referred to as a first etching solution. Thereafter, the resist pattern 151 is removed with an organic solvent or the like.

  Next, as shown in FIG. 9A, a resist pattern 152 is formed in a region where the first surface emitting laser 11 and the second surface emitting laser 12 are formed. Specifically, a photoresist is applied on the fourth adjustment layer 114 and the third adjustment layer 113 of the wavelength adjustment layer 110, and exposure and development are performed by an exposure apparatus, thereby forming a resist pattern 152.

  Next, as shown in FIG. 9B, the third adjustment layer 113 in the region where the resist pattern 152 is not formed is removed by wet etching. Specifically, since the third adjustment layer 113 is formed of GaInP, wet etching is performed using a mixed solution of hydrochloric acid and water. As a result, only the third adjustment layer 113 in the region where the resist pattern 152 is not formed is removed, and the surface of the second adjustment layer 112 is exposed. This mixed solution can etch GaInP, but GaAsP forming the second adjustment layer 112 can hardly be etched. This mixed solution may be referred to as a second etching solution. Thereafter, the resist pattern 152 is removed with an organic solvent or the like.

  Next, as shown in FIG. 9C, a resist pattern 153 is formed in a region where the first surface emitting laser 11, the second surface emitting laser 12, and the third surface emitting laser 13 are formed. Specifically, a photoresist is applied on the fourth adjustment layer 114, the third adjustment layer 113, and the second adjustment layer 112 of the wavelength adjustment layer 110, and exposure and development are performed by an exposure apparatus, thereby providing a resist. A pattern 153 is formed.

  Next, as shown in FIG. 10A, the second adjustment layer 112 in a region where the resist pattern 153 is not formed is removed by wet etching. Specifically, the second adjustment layer 112 in the region where the resist pattern 153 is not formed is removed with the first etching solution. As a result, only the second adjustment layer 112 in the region where the resist pattern 153 is not formed is removed, and the surface of the first adjustment layer 111 is exposed. Thereafter, the resist pattern 153 is removed with an organic solvent or the like.

  Next, as shown in FIG. 10B, the upper DBR 106 is formed. Specifically, on each wavelength adjustment layer 110, a dielectric film made of a high refractive index material made of oxide, nitride, fluoride, etc. and a dielectric film made of a low refractive index material are formed by sputtering or the like. It is formed by alternately laminating every predetermined film thickness.

  Thereby, the wavelength adjustment layer 110 and the upper DBR 106 in the surface emitting laser element according to the present embodiment can be formed.

  In the present embodiment, unlike Patent Documents 3 and 7, the first adjustment layer 111, the second adjustment layer 112, the third adjustment layer 113, and the fourth adjustment layer 114 that become the wavelength adjustment layer 110 are provided. Since it does not contain Al, it is difficult to be oxidized after etching, and a clean surface state can be maintained after etching. That is, since Al is very easily corroded, when any of the first adjustment layer 111, the second adjustment layer 112, the third adjustment layer 113, and the fourth adjustment layer 114 is formed of a material containing Al. The surface state after performing wet etching or the like becomes inferior, and even if the upper DBR 106 is formed thereon, the surface state may be peeled off, or the thickness of the resonator region may be uneven. However, in the surface emitting laser element according to the present embodiment, since the wavelength adjustment layer 110 is formed of a material that does not contain Al, Al corrosion or the like does not occur, and such a problem does not occur.

  In the present embodiment, the wavelength adjustment layer 110 is formed by alternately forming GaAsP and GaInP. When wet etching is performed, one can be etched but the other is etched. Etching is performed using two kinds of etching solutions that cannot be performed. By performing etching using these two kinds of etching solutions, the surface after etching becomes flat and can be formed with a predetermined thickness without being over-etched. Thereby, a surface emitting laser element with stable characteristics can be obtained.

  In addition, as in Patent Documents 3 and 7, when the epitaxial wafer is processed (the wavelength adjustment layer is processed) and then the upper DBR is regrown, the flatness and crystallinity on the etching step in the regrown layer are formed. Such as bad. In contrast, in the present embodiment, even when the wavelength adjustment layer is processed, such an inconvenience does not occur because the upper DBR is formed of a dielectric.

(Surface emitting laser element)
Next, the surface-emitting laser element in the present embodiment will be described in more detail based on FIG. 11 is a cross-sectional view taken along one-dot chain line 6A-6B in FIG. This surface emitting laser element is a surface emitting laser in which an AlAs layer serving as a current confinement layer is selectively oxidized to form a current confinement structure, and the oscillation wavelength is 894.6 nm. Specifically, four surface emitting lasers are formed on a 300 μm square semiconductor chip (substrate). As described above, in the surface emitting laser element, since a plurality of surface emitting lasers can be formed in a narrow region, even when the surface emitting laser to emit light is switched, the light emission position hardly changes. Therefore, optical axis adjustment or the like is unnecessary or extremely easy. For this reason, the size of the substrate is preferably 500 μm × 500 μm or less.

In the present embodiment, the substrate 101 is an n-GaAs substrate. The lower DBR 102 includes an n-Al _0.1 Ga _0.9 As high-refractive index layer and an n-Al _0.9 Ga _0.1 As low-refractive index layer, each having an optical film thickness of λ. It is formed by laminating 35.5 pairs so as to be / 4.

An active layer 103 made of a GaInAs quantum well layer / GaInPAs barrier layer is formed on the lower DBR 102 via a lower spacer layer 121 made of Al _0.2 Ga _0.8 As. On the active layer _103, second upper spacer made of Al 0.2 _{Ga 0.8} current confining layer ₁₂₃ made of the first upper spacer layer 122, AlAs consisting _As, Al 0.2 _{Ga 0.8} As The layer 124 and the contact layer 125 made of p-GaAs are sequentially stacked. The contact layer 125 is the same as the contact layer 105 in the first embodiment.

  On the contact layer 125, GaAsP and GaInP are alternately stacked to form a wavelength composed of the first adjustment layer 111, the second adjustment layer 112, the third adjustment layer 113, and the fourth adjustment layer 114. The adjustment layer 110 is formed, and as described above, a part of the wavelength adjustment layer 110 in a predetermined region is removed corresponding to each surface emitting laser. The lower DBR 102, the lower spacer layer 121, the active layer 103, the first upper spacer layer 122, the current confinement layer 123, the second upper spacer layer 124, the contact layer 125, and the wavelength adjustment layer 110 are made of semiconductors by MOCVD or MBE. It is formed by epitaxially growing the material.

  In the surface emitting laser element according to the present embodiment, each surface emitting laser has a mesa structure, and this mesa structure is formed by etching a semiconductor layer between the surface emitting lasers to be formed. After the mesa structure is formed, heat treatment is performed in water vapor to oxidize the non-oxidized current confinement layer 123 from the periphery of the mesa structure, and a selective oxidation region 123a (oxidized region) and a central portion of the peripheral portion. The non-oxidized current confinement region 123b is formed. That is, the current confinement layer 123 includes an oxidized selective oxidation region 123a and an unoxidized current confinement region 123b, and has a current confinement structure. In the present embodiment, the mesa structure as viewed from above has a circular shape, but may be formed to have an elliptical shape, a square shape, a rectangular shape, or the like.

In addition, on the wavelength adjustment layer 110 removed by etching corresponding to each surface emitting laser, the upper DBR 106 includes an optical film of each of the TiO ₂ high refractive index layer and the SiO ₂ low refractive index layer. It is formed by laminating 8.5 pairs so that the thickness becomes λ / 4. The upper DBR 106 is a dielectric material and may be formed by stacking a high refractive index material and a low refractive index material. Specifically, an oxide, nitride, fluoride, or the like is used. Can be mentioned. Examples of the high refractive index material include Ta ₂ O ₅ and HfO _{2 in} addition to TiO ₂ . Examples of the low refractive index material include MgF _{2 and the} like in addition to SiO ₂ .

  In the surface emitting laser element according to the present embodiment, the wavelength adjustment layer 110 and the upper DBR 106 are formed in a region narrower than the region where the contact layer 125 is formed in each surface emitting laser. That is, the wavelength adjustment layer 110 and the upper DBR 106 are formed so that a part of the surface of the contact layer 125 is exposed. In this embodiment, a resonator region is formed by the active layer 103, the wavelength adjustment layer 110, and the like formed between the lower DBR 102 and the upper DBR 106. Further, several pairs of DBRs in which semiconductor layers having different refractive indexes are stacked may be formed between the active layer 103 and the contact layer 125, and the effect of the wavelength adjusting layer can be obtained.

  Thereafter, a protective film 126 made of SiN having an optical film thickness of λ / 4 is formed on the entire surface, and the protective film 126 in the region where the upper electrode 131 is formed on the contact layer 125 is removed, and the p-side electrode The upper electrode 131 is formed. The upper electrode 131 is formed corresponding to each surface emitting laser, and each upper electrode 131 is connected to each electrode pad 21 to 24 shown in FIG. In addition, a lower electrode 132 serving as an n-side electrode is formed on the back surface of the substrate 101, and a groove between the mesa structure and the mesa structure is filled with polyimide 127. The lower electrode is not only formed on the back surface of the substrate, such as an intracavity contact structure, but also has a structure in which a contact layer is formed between the lower DBR 102 and the active layer 103 and connected to this contact layer. There may be.

  On the upper DBR 106, a light shielding portion 107 having an opening 108 in the center is formed. The light shielding portion 107 is formed of a metal material, and is formed of, for example, a laminated film of Cr (lower layer) and Au (upper layer). In the present embodiment, light from the surface emitting laser element is emitted from the opening 108. The reason why Cr is used as a lower layer is to improve the adhesion with the dielectric film forming the upper DBR 106, and Ti or the like may be used instead of Cr. The light shielding portion 107 can be formed by a lift-off method. Specifically, a photoresist is coated on the upper DBR 106, and exposure and development are performed by an exposure apparatus to form a resist pattern having an opening in a region where the light shielding portion 107 is formed. After forming a Cr film and an Au film, the film is immersed in an organic solvent or the like, and the Cr film and the Au film are removed together with the resist pattern.

  Although the case where the upper electrode 131 serving as the p-side electrode and the light shielding portion 107 are formed separately has been described, the upper electrode 131 and the light shielding portion 107 may be formed simultaneously, and in this case, the upper electrode 131 and the light shielding portion 107 may be formed simultaneously. You may form so that the part 107 may be united. In the surface emitting laser according to the present embodiment, the upper electrode 131 is not formed on the upper DBR 106, and only the light shielding portion 107 is formed. Thus, by forming the light shielding part 107 having the opening 108 on the upper DBR 106, the divergence angle of the light emitted from the opening 108 can be widened.

  The surface emitting laser element in the present embodiment emits laser light having different wavelengths λ1, λ2, etc. for each surface emitting laser in the direction indicated by the arrow. Further, SiN serving as the protective film 126 has a function as an upper reflecting mirror and also has a function of improving reliability because it covers a layer containing Al exposed at the side surface when forming a mesa structure.

  In the surface emitting laser element according to the present embodiment, the upper DBR 106 is formed by stacking dielectric films having different refractive indexes, so that the refractive index difference is higher than that of stacking semiconductor materials having different refractive indexes. Can be greatly increased. Thereby, the number of stacked layers in the upper DBR 106 can be reduced, and furthermore, the optical thickness in the upper DBR 106 can be reduced.

  In the surface emitting laser according to the present embodiment, the upper electrode 131 is formed on the contact layer 125 in each surface emitting laser formed under the wavelength adjustment layer 110. For this reason, an electric current can be evenly supplied to each surface emitting laser without being affected by the thickness of the wavelength adjustment layer 110. That is, when the upper electrode is formed on the wavelength adjustment layer and brought into direct contact with the wavelength adjustment layer, the material to be contacted differs depending on the element, so that the resistance at the contact portion differs, or the thickness of the wavelength adjustment layer The amount of current that can be supplied to each surface emitting laser may vary depending on the current. Therefore, in these cases, the electrical characteristics and light emission characteristics of each surface emitting laser are also greatly different. Further, when a contact layer is formed on the wavelength adjustment layer and an upper electrode is formed thereon, the electric resistance increases due to band discontinuity at the interface between the layers forming the wavelength adjustment layer. Moreover, since the number of interfaces differs depending on the surface emitting laser, the resistance value also varies depending on the surface emitting laser. However, in the surface emitting laser element according to the present embodiment, the upper electrode 131 is connected to the contact layer 125 formed under the wavelength adjustment layer 110, and thus does not depend on the thickness of the wavelength adjustment layer 110. Each surface emitting laser is formed at the same position. Therefore, the electrical characteristics of the surface emitting lasers can be made substantially uniform, so that the characteristics do not vary greatly depending on the wavelength of light emitted.

  The contents other than the above are the same as in the first embodiment.

[Third Embodiment]
Next, a third embodiment will be described. Unlike the second embodiment, the present embodiment has a structure in which the light shielding portion is provided under the DBR made of a dielectric material. The surface emitting laser element in the present embodiment will be described with reference to FIG.

  FIG. 12 is a cross-sectional view taken along a portion corresponding to the alternate long and short dash line 6A-6B in FIG. 6 of the second embodiment. The surface emitting laser element according to the present embodiment is a surface emitting laser having a current confinement structure formed by selectively oxidizing an AlAs layer serving as the current confinement layer 123 and having an oscillation wavelength of 894.6 nm. .

  Specifically, four surface emitting lasers 11a and 12a are formed on a 300 μm square semiconductor chip (substrate). As described above, in the surface emitting laser element according to the present embodiment, a plurality of surface emitting lasers can be formed in a narrow region. Therefore, even when the surface emitting laser to emit light is switched, the emission position is almost the same. Absent. Therefore, optical axis adjustment or the like is unnecessary or extremely easy. Therefore, the size of the substrate 101 is preferably 500 μm × 500 μm or less.

In the present embodiment, the substrate 101 is an n-GaAs substrate. The lower DBR 102 includes an n-Al _0.1 Ga _0.9 As high-refractive index layer and an n-Al _0.9 Ga _0.1 As low-refractive index layer, each having an optical film thickness of λ. It is formed by laminating 35.5 pairs so as to be / 4.

An active layer 103 made of a GaInAs quantum well layer / GaInPAs barrier layer is formed on the lower DBR 102 via a lower spacer layer 121 made of Al _0.2 Ga _0.8 As. Further, on the active layer _103, Al 0.2 _{Ga 0.8} first upper spacer layer 122 made of As, the current confinement layer ₁₂₃ made of _AlAs, Al 0.2 _{Ga 0.8} As from the consisting second The upper spacer layer 124 and the contact layer 125 made of p-GaAs are sequentially stacked.

  On the contact layer 125, GaAsP and GaInP are alternately laminated to form a first adjustment layer 161, a second adjustment layer 162, a third adjustment layer 163, a fourth adjustment layer 164, and the like. A wavelength adjustment layer 160 is formed, and as described above, a part of the wavelength adjustment layer 160 in a predetermined region is removed corresponding to each of the surface emitting lasers 11a, 12a and the like. Note that the lower DBR 102, the lower spacer layer 121, the active layer 103, the first upper spacer layer 122, the current confinement layer 123, the second upper spacer layer 124, the contact layer 125, and the wavelength adjustment layer 160 are made of semiconductors by MOCVD or MBE. It is formed by epitaxially growing the material.

  In the surface emitting laser element according to the present embodiment, each of the surface emitting lasers 11a and 12a has a mesa structure, and this mesa structure is formed by etching a semiconductor layer between the formed surface emitting lasers. Is done. After the mesa structure is formed, heat treatment is performed in water vapor to oxidize the non-oxidized current confinement layer 123 from the periphery of the mesa structure, thereby selectively oxidizing the peripheral portion (oxidized region) 123a and the central portion. The non-oxidized current confinement region 123b is formed. That is, in the current confinement layer 123, a current confinement structure is formed by the oxidized selective oxidation region 123a and the non-oxidized current confinement region 123b. In addition, the shape seen from the upper part of the mesa structure may be formed so as to be circular, or may be formed so as to have an elliptical shape, a square shape, a rectangular shape, or the like. Good.

  A protective film 126 made of SiN is formed on the entire semiconductor layer, but the protective film 126 in the region where the wavelength adjustment layer 160 and the upper electrode 181 are formed on the contact layer 125 is removed.

  Thereafter, an upper electrode 181 serving as a p-side electrode is formed. The upper electrode 181 is formed corresponding to each surface emitting laser, and each upper electrode 181 is connected to an electrode pad. As a material for forming the upper electrode 181, a stacked metal film of Ti / Pt / Au, Cr / AuZn / Au, or the like can be used. Specifically, after the resist pattern is formed, the above-described laminated metal film is formed, and then immersed in an organic solvent to remove the metal film formed on the resist pattern. It can be formed by a method or the like. The upper electrode 181 has a light shielding function, and thus also serves as a light shielding part.

Further, on the wavelength adjustment layer 160 removed by etching corresponding to each of the surface emitting lasers 11a, 12a, etc., a TiO ₂ high refractive index layer and a SiO ₂ low refractive index layer are optically connected to each layer. The upper DBR 170 is formed by laminating 8.5 pairs so that the film thickness becomes λ / 4. The upper DBR 170 may be a dielectric material formed by laminating a high refractive index material and a low refractive index material. Specifically, an oxide, nitride, fluoride, or the like is used. Can be mentioned. Examples of the high refractive index material include Ta ₂ O ₅ and HfO _{2 in} addition to TiO ₂ . Examples of the low refractive index material include MgF _{2 and the} like in addition to SiO ₂ . At this time, the upper DBR 170 made of a dielectric material may also be formed on a part of the upper electrode 181 that also serves as a light shielding portion, as shown in FIG.

  In the surface emitting laser element according to the present embodiment, the wavelength adjustment layer 160 is formed in a region narrower than the region where the contact layer 125 is formed in each surface emitting laser. That is, the wavelength adjustment layer 160 is formed so that a part of the surface of the contact layer 125 is exposed. Thus, the upper electrode 181 is formed on the contact layer 125 in the region where the wavelength adjustment layer 160 is not formed. In this embodiment, a resonator region is formed by the active layer 103, the wavelength adjustment layer 160, and the like formed between the lower DBR 102 and the upper DBR 170. Further, several pairs of DBRs in which semiconductor layers having different refractive indexes are stacked may be formed between the active layer 103 and the contact layer 125. In this case as well, the effect of the wavelength adjustment layer 160 can be obtained. .

  In addition, a lower electrode 132 serving as an n-side electrode is formed on the back surface of the substrate 101, and a groove between the mesa structure and the mesa structure is filled with polyimide 127. In the surface emitting laser element according to the embodiment, the lower DBR 102 and the active layer 103 are not limited to the structure in which the lower electrode 132 is formed on the back surface of the substrate 101 but also the intracavity contact structure. A structure in which a contact layer (not shown) is formed between them and a lower electrode 132 is formed so as to be connected to the contact layer (not shown).

  The surface emitting laser element according to the present embodiment emits laser light having different wavelengths λ1 and λ2 for each of the surface emitting lasers 11a and 12a in the direction indicated by the arrow. Further, SiN serving as the protective film 126 has a function of improving reliability because it covers a layer containing Al exposed at the side surface when forming the mesa structure.

In the surface emitting laser element according to the present embodiment, the divergence angle of the emitted light can be widened by the upper electrode 181 that also serves as a light shielding portion. FIG. 13 shows the upper electrode opening area dependency of the divergence angle (the angle at which the intensity of the emitted light is 1 / e ² or more). It can be seen that when the area of the upper electrode opening is smaller than 30 μm ² , the divergence angle becomes larger than 20 deg. The upper electrode opening is an opening formed inside the upper electrode 181.

  Since the upper DBR 170 is formed by stacking dielectric films having different refractive indexes, the refractive index difference can be made larger than that formed by stacking semiconductor materials having different refractive indexes. Thereby, the number of stacked layers in the upper DBR 170 can be reduced, and further, the upper DBR 170 can be formed thin.

  In the surface emitting laser element according to the present embodiment, the upper electrode 181 and the wavelength adjustment layer 160 are formed on the contact layer 125. Therefore, it is possible to allow a current to flow evenly to each surface emitting laser without being affected by the thickness of the wavelength adjustment layer 160. That is, when the upper electrode is formed on the wavelength adjustment layer and brought into direct contact with the wavelength adjustment layer, the material to be contacted differs depending on the element, so that the resistance at the contact portion differs, or the thickness of the wavelength adjustment layer The amount of current that can be supplied to each surface emitting laser may vary depending on the current. Therefore, in these cases, the electrical characteristics and light emission characteristics of each surface emitting laser are also greatly different. Further, when a contact layer is formed on the wavelength adjustment layer and an upper electrode is formed thereon, the electric resistance increases due to band discontinuity at the interface between the layers forming the wavelength adjustment layer. Moreover, since the number of interfaces differs depending on the surface emitting laser, the resistance value also varies depending on the surface emitting laser. However, since the upper electrode 181 is connected to the contact layer 125 formed under the wavelength adjustment layer 160 in the surface emitting laser element according to the present embodiment, these can be avoided. In the present embodiment, the upper DBR includes a dielectric, and a light-shielding portion is provided between the semiconductor and the dielectric, which is different from Patent Document 6 in which the upper DBR is entirely a semiconductor. .

[Fourth Embodiment]
Next, a fourth embodiment will be described. Based on FIG. 14, the surface emitting laser element in the present embodiment will be described. The surface emitting laser element 200 in the present embodiment has eight surface emitting lasers on a substrate 201, and emits light having different wavelengths.

  Specifically, the surface emitting laser element 200 according to the present embodiment includes a first surface emitting laser 211, a second surface emitting laser 212, a third surface emitting laser 213, and a fourth surface emitting light on a substrate 201. A laser 214, a fifth surface emitting laser 215, a sixth surface emitting laser 216, a seventh surface emitting laser 217, and an eighth surface emitting laser 218 are provided. The first surface emitting laser 211 to the eighth surface emitting laser 218 are each connected to an electrode pad. Specifically, an electrode pad 221 is connected to the first surface emitting laser 211, an electrode pad 222 is connected to the second surface emitting laser 212, and a third surface emitting laser 213 is connected to the third surface emitting laser 213. The electrode pad 223 is connected, the electrode pad 224 is connected to the fourth surface emitting laser 214, the electrode pad 225 is connected to the fifth surface emitting laser 215, and the sixth surface emitting laser is connected. An electrode pad 226 is connected to the laser 216, an electrode pad 227 is connected to the seventh surface emitting laser 217, and an electrode pad 228 is connected to the eighth surface emitting laser 218.

  Further, the first surface emitting laser 211 to the eighth surface emitting laser 218 have different wavelengths from each other. That is, the wavelength λ1 emitted from the first surface emitting laser 211, the wavelength λ2 emitted from the second surface emitting laser 212, the wavelength λ3 emitted from the third surface emitting laser 213, and the fourth surface emitting laser. 214, wavelength λ5 emitted from the fifth surface emitting laser 215, wavelength λ6 emitted from the sixth surface emitting laser 216, wavelength λ7 emitted from the seventh surface emitting laser 217, The wavelengths λ8 emitted from the eighth surface emitting laser 218 are different from each other. Thus, in order to emit light of different wavelengths in each surface emitting laser, a wavelength adjusting layer is provided in the same manner as in the second embodiment, and the thickness of the wavelength adjusting layer is changed for each surface emitting laser. Formed. Of course, the total number in the wavelength adjustment layer is increased. The electrode pads 221 to 228 each have a size of about 50 μm square, and the substrate 201 is a semiconductor chip having a size of 300 μm square.

  In the surface emitting laser element according to the present embodiment, since it is possible to select from more wavelengths, the yield can be further improved. Further, in the surface emitting laser element in the present embodiment, not only the element having the wavelength closest to the required wavelength but also the element having the second closest wavelength may be used, and by using it as a spare surface emitting laser. The life can be extended.

  The contents other than the above are the same as those in the second embodiment.

[Fifth Embodiment]
Next, a fifth embodiment will be described. Based on FIG. 15, the surface emitting laser element in the present embodiment will be described. The surface-emitting laser element 300 in this embodiment has eight surface-emitting lasers on a substrate 301, and two surface-emitting lasers that emit the same wavelength are formed.

  Specifically, the surface emitting laser element 300 according to the present embodiment includes a first surface emitting laser 311, a second surface emitting laser 312, a third surface emitting laser 313, and a fourth surface emitting light on a substrate 301. A laser 314, a fifth surface emitting laser 315, a sixth surface emitting laser 316, a seventh surface emitting laser 317, and an eighth surface emitting laser 318 are included. The first surface emitting laser 311 to the eighth surface emitting laser 318 are each connected to an electrode pad. Specifically, an electrode pad 321 is connected to the first surface emitting laser 311, an electrode pad 322 is connected to the second surface emitting laser 312, and the third surface emitting laser 313 is connected to the third surface emitting laser 313. An electrode pad 323 is connected, an electrode pad 324 is connected to the fourth surface emitting laser 314, an electrode pad 325 is connected to the fifth surface emitting laser 315, and a sixth surface emitting laser is connected. An electrode pad 326 is connected to the laser 316, an electrode pad 327 is connected to the seventh surface emitting laser 317, and an electrode pad 328 is connected to the eighth surface emitting laser 318.

  The first surface emitting laser 311 to the eighth surface emitting laser 318 are formed so that two lasers having the same wavelength are provided. Specifically, the light emitted from the first surface emitting laser 311 and the second surface emitting laser 312 has the same wavelength λ1, and the light emitted from the third surface emitting laser 313 and the fourth surface emitting laser 314. Are the same wavelength λ2, the light emitted from the fifth surface emitting laser 315 and the sixth surface emitting laser 316 is the light emitted from the same wavelength λ3, the seventh surface emitting laser 317 and the eighth surface emitting laser 318. Are the same wavelength λ4, and the wavelengths λ1 to λ4 are mutually different wavelengths. Thus, in order to emit light of different wavelengths in each surface emitting laser, a wavelength adjusting layer is provided in the same manner as in the second embodiment, and the thickness of the wavelength adjusting layer is changed for each surface emitting laser. Formed. The electrode pads 321 to 328 each have a size of about 50 μm square, and the substrate 301 is a semiconductor chip having a size of 300 μm square.

  In the surface emitting laser element according to the present embodiment, since there are two surface emitting lasers that emit light of the same wavelength, among surface emitting lasers that emit light of the same wavelength due to defects or failures, Even if one stops emitting light, the other can be used. Therefore, the lifetime of the surface emitting laser element can be extended and the yield can be further improved. Further, in the surface emitting laser element in the present embodiment, not only the element having the wavelength closest to the required wavelength but also the element having the second closest wavelength may be used, and by using it as a spare surface emitting laser. The life can be extended.

  The contents other than the above are the same as those in the second embodiment.

[Sixth Embodiment]
Next, a sixth embodiment will be described. The present embodiment is an atomic oscillator using the surface emitting laser element in the first to fifth embodiments. The atomic oscillator in the present embodiment will be described based on FIG. The atomic oscillator in this embodiment is a CPT-type small atomic oscillator and includes a light source 410, a collimating lens 420, a λ / 4 plate 430, an alkali metal cell 440, a photodetector 450, and a modulator 460.

  As the light source 410, the surface emitting laser element in the first to fifth embodiments is used. The alkali metal cell 440 is filled with Cs (cesium) atomic gas as an alkali metal, and uses the transition of the D1 line. The photodetector 450 uses a photodiode.

  In the atomic oscillator in this embodiment, the light emitted from the light source 410 is irradiated to the alkali metal cell 440 in which the cesium atom gas is enclosed, and the electrons in the cesium atom are excited. The light transmitted through the alkali metal cell 440 is detected by the photodetector 450, and the signal detected by the photodetector 450 is fed back to the modulator 460, and the surface emitting laser element in the light source 410 is modulated by the modulator 460.

  The surface emitting laser elements in the first to fifth embodiments emit light having a wide divergence angle, for example, a divergence angle of 20 ° or more, and further 30 ° or more. The distance Xa with the collimating lens 420 can be shortened, and the atomic oscillator can be made smaller.

  The atomic oscillator in the present embodiment will be described more specifically with reference to FIG. 17. The atomic oscillator in the present embodiment is formed on the circuit board 471 in the vertical direction. An alumina substrate 472 is provided on the circuit board 471, and the surface emitting laser elements in the first to fifth embodiments serving as the light source 410 are installed on the alumina substrate 472. The alumina substrate 472 is provided with a surface emitting laser heater 473 for controlling the temperature of the light source 410 and the like. An ND (Neutral Density) filter 474 is provided above the light source 410. The ND filter 474 is installed at a predetermined position by a heat insulating spacer 475 made of glass or the like. A collimator lens 420 is provided above the ND filter 474, and a λ / 4 plate 430 is provided above the collimator lens. The λ / 4 plate 430 is installed at a predetermined position by a spacer 476 formed of silicon or the like. An alkali metal cell 440 is provided on the λ / 4 plate 430. The alkali metal cell 440 includes two glass substrates 441. The two glass substrates 441 are opposed to each other, the edge portions are connected by the silicon substrate 442, and the glass substrate 441 and the silicon substrate 441 are connected to each other. A portion surrounded by the substrate 442 is filled with alkali metal. Note that in the alkali metal cell 440, a surface through which laser light is transmitted is formed by the glass substrate 441. Cell heaters 477 are provided on both sides of the alkali metal cell 440, and the alkali metal cell 440 can be set to a predetermined temperature. A photo detector 450 is provided above the alkali metal cell 440, and the photo detector 450 is installed at a predetermined position by a spacer 478 made of silicon.

  Next, FIG. 18 shows a structure of atomic energy levels related to CPT. Utilizing the fact that the light absorptance decreases when electrons are excited simultaneously from two ground levels to the excited level. The surface emitting laser uses an element having a carrier wavelength close to 894.6 nm. The wavelength of the carrier wave can be tuned by changing the temperature or output of the surface emitting laser. As shown in FIG. 19, by applying modulation, sidebands are generated on both sides of the carrier, and the frequency difference is modulated at 4.6 GHz so that the frequency difference matches the natural frequency of 9.2 Cs atoms. . As shown in FIG. 20, the laser light passing through the excited Cs gas is maximized when the sideband frequency difference matches the natural frequency difference of the Cs atoms, so the output of the photodetector 450 holds the maximum value. As described above, the modulator 460 feeds back to adjust the modulation frequency of the surface emitting laser element in the light source 410. Since the natural frequency of the atom is extremely stable, the modulation frequency becomes a stable value, and this information is extracted as an output. When the wavelength is 894.6 nm, a wavelength in the range of ± 1 nm (more preferably ± 0.3 nm) is required.

  The atomic oscillator in the present embodiment can be miniaturized by using the surface emitting laser elements in the first to fifth embodiments. Further, by using the surface emitting laser elements according to the second to fifth embodiments, an atomic oscillator can be manufactured and provided at a low cost. Furthermore, by using the surface emitting laser element in the fourth embodiment and the fifth embodiment, an atomic oscillator having a longer lifetime can be provided.

In this embodiment, Cs is used as the alkali metal, and a surface emitting laser having a wavelength of 894.6 nm is used to use the transition of the D1 line. However, when using the C2 D2 line, 852.3 nm is used. You can also. Rb (rubidium) can also be used as the alkali metal, and 795.0 nm can be used when the D1 line is used, and 780.2 nm can be used when the D2 line is used. The material composition of the active layer can be designed according to the wavelength. The modulation frequency when using Rb is modulated at 3.4 GHz for ⁸⁷ Rb and 1.5 GHz for ⁸⁵ Rb. Even in these wavelengths, a wavelength in the range of ± 1 nm is required.

  As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention. Further, in the embodiment according to the present invention, the case where the surface emitting laser element is used for the atomic oscillator has been described. However, the surface emitting laser element in the second to fifth embodiments has a predetermined wavelength such as a gas sensor. It can be used for other devices that require a large amount of light. In this case, in these apparatuses and the like, the same effect can be obtained by using surface emitting laser light having a predetermined wavelength according to the application.

DESCRIPTION OF SYMBOLS 10 Surface emitting laser element 11 Surface emitting laser 12 Surface emitting laser 13 Surface emitting laser 14 Surface emitting laser 21 Electrode pad 22 Electrode pad 23 Electrode pad 24 Electrode pad 101 Substrate 102 Lower DBR
103 Active layer 105 Contact layer 106 Upper DBR
107 light shielding portion 108 opening portion 110 wavelength adjustment layer 123a selective oxidation region 123b current confinement region 131 upper electrode 132 lower electrode 410 light source 420 collimator lens 430 λ / 4 plate 440 alkali metal cell 450 photodetector 460 modulator

JP 2008-53353 A JP 2000-58958 A JP 11-330631 A JP 2008-283129 A JP 2009-188598 A JP 2002-208755 A Japanese Patent No. 2751814

Applied Physics Letters, Vol. 85, pp. 1460-1462 (2004). Comprehensive Microsystems, vol. 3, pp. 571-612 Proc. of SPIE Nol. 6132 613208-1 (2006)

Claims (22)

A lower DBR formed on the substrate;
An active layer formed on the lower DBR;
An upper DBR formed on the active layer;
Have
The upper DBR includes a dielectric multilayer film formed by alternately laminating dielectrics having different refractive indexes,
A light shielding portion is formed on the upper DBR,
A surface emitting laser element having an opening for emitting light at a central portion of the light shielding portion. A lower DBR formed on the substrate;
An active layer formed on the lower DBR;
An upper DBR formed on the active layer;
Have
The upper DBR includes a dielectric multilayer film formed by alternately laminating dielectrics having different refractive indexes,
A light shielding portion is formed on the active layer and below the dielectric multilayer film,
A surface emitting laser element having an opening for emitting light at a central portion of the light shielding portion. The light emitted from the opening by the light shielding portion has an intensity (divergence angle) of 20 deg or more at an intensity 1 / e ² . Surface emitting laser element. The surface emitting laser element according to claim 1, wherein an area of the opening is 30 μm ² or less. The surface emitting laser element according to claim 1, wherein an area of the opening is 20 μm ² or less.   The surface emitting laser element according to claim 1, wherein the light shielding portion is formed of a metal material or a material that absorbs the light. A contact layer is formed between the active layer and the dielectric portion of the upper DBR,
The surface emitting laser element according to claim 1, wherein one electrode is connected to the contact layer. A wavelength adjusting layer is provided between the active layer and the dielectric portion of the upper DBR;
The surface emitting laser element according to claim 1, comprising a plurality of surface emitting lasers each emitting different wavelengths by changing the thickness of the wavelength adjusting layer. A contact layer is formed between the active layer and the wavelength adjustment layer,
9. The surface emitting laser element according to claim 8, wherein one electrode is connected to the contact layer.   10. The surface emitting laser element according to claim 7, wherein the contact layer is made of a material containing GaAs.   The wavelength adjustment layer is formed of a film in which GaInP and GaAsP are alternately laminated, or a film in which GaInP and GaAs are alternately laminated, and a part of the laminated film is formed for each layer. The surface emitting laser element according to claim 8 or 9, wherein the film thickness of the wavelength adjusting layer is changed by removing the wavelength adjusting layer.   The removal of the laminated film in the wavelength adjustment layer is performed by wet etching, and includes a first etching solution for etching to remove the GaInP and a second etching for etching the GaAsP or the GaAs. The surface emitting laser according to claim 11, wherein the etching solution is different from the etching solution. The substrate is a conductive semiconductor crystal substrate,
The surface light emission according to any one of claims 8, 9, 11 and 12, wherein the lower DBR, the active layer, and the wavelength adjustment layer are formed by epitaxially growing a semiconductor material. Laser element.   The surface emitting laser element according to any one of claims 8, 9, and 11 to 13, wherein the plurality of surface emitting lasers all emit light having different wavelengths.   The surface emitting laser element according to any one of claims 8, 9, and 11 to 13, wherein the plurality of surface emitting lasers include a plurality of surface emitting lasers that emit light having the same wavelength.   16. The surface according to claim 8, wherein any one of the plurality of wavelengths is 780.2 nm, 795.0 nm, 852.3 nm, and 894.6 nm. Light emitting laser element.   The surface emitting laser according to claim 1, wherein the dielectric contains an oxide, a nitride, or a fluoride.   The surface-emitting laser element according to claim 1, wherein the active layer contains GaInAs.   19. The surface emitting laser element according to claim 1, wherein the size of the substrate is smaller than 500 [mu] m * 500 [mu] m. A surface emitting laser element according to any one of claims 1 to 19,
An alkali metal cell encapsulating an alkali metal;
A light detector that detects light transmitted through the alkali metal cell out of light irradiated to the alkali metal cell from the surface emitting laser in the surface emitting laser element;
Of the light including the sideband emitted from the surface emitting laser, and by making light of two different wavelengths incident on the alkali metal cell, the light absorption characteristics due to the quantum interference effect by two types of resonance light An atomic oscillator characterized by controlling a modulation frequency.   21. The atomic oscillator according to claim 20, wherein the two light beams having different wavelengths are sideband light beams emitted from the surface emitting laser.   The atomic oscillator according to claim 20 or 21, wherein the alkali metal is rubidium or cesium.

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